Production of trialkoxy tetrahydrofurans



nited PRODUCTION OF TRIALKOXY TETRAHYDROFUS Niels Konrad Friedrich Wilhelm Clauson-Kaas, Haifa,

Israel, assignor to A/S Sadoiin & Holmblad, Copenhagen, Denmark No Drawing. Application January 17, 1956 Serial No. 559,540

This application is a continuation-in-part of my parent applications Serial No. 295,125, filed June 23, 1952 and Serial No. 403,461, filed January 11, 1954, both now abandoned.

This present invention relates to 6-lower alkoxy tropinones, to the tri(lower alkoxy)tetrahydrofuran (and alcoholysates thereof) intermediates therefor, and to methods of producing these compounds.

It is an object of this invention to provide 6-lower alkoxy tropinones, new compounds which are useful in the tropa alkaloid field as intermediates in the preparation of the known alkaloids (e.g. 6-hydroxytropinone and valeroidine).

Another object of this invention is the provision of a group of hitherto unknown compounds which are tri(loweralkoxy) tetrahydrofurans and their alcoholysates, such compounds being liquid, colorless products which are useful as solvents for high temperature reactions such as Grignard reactions, and as intermediates in the production of (lower alkoxy)-succinic dialdehydes, from which the 6-lower alkoxy tropinones can be produced by known methods.

Another object of this invention is the provision of a method for the production of the said compounds.

These and other objects will appear from the following detailed description of the invention, which description, however, is not to be considered limitative of the scope of the invention, since obvious modifications and chemical equivalents will be apparent to those skilled in the art.

According to one aspect of this invention, it has been found that on reacting 2,5-di(lower alkoxy)-2,5-dihydrofurans with an alcohol in the presence of a strong acid, the alcohol is added to the double bond of the dihydrofuran. The action of the acid in the presence of an alcohol may further result in an alcoholysis, whereby the furan ring is opened.

Thus, the reaction mixture will generally contain a mixture of components. In order to isolate these components or some of them, the reaction mixture is fractionally distilled. Since, however, the different compounds of the mixture often have close boiling points, it may be expedient to add an alkoxide before the distillation in order to destroy components with free or hydrated aldehyde groups, or with semi-acetal groups. I

It has been found that when the acid is boron trifluoride, particularly good yields of the desired acetals are obtained. However, satisfactory yields may also be obtained by the use of other strong acids, for instance sulfuric acid and hydrochloric acid.

The alcohol is preferably a lower alkanol, for instance methanol, isopropanol, butanol or hexanol. Other alcohols, such as araliphatic alcohols (for instance benzyl alcohol) might be used.

and

EOALOJVOE anon ice The alcohol addition is illustrated by the following schemes of reaction, where E is an ethyl group:

and

+ non m-( mom CH0 one The 2,3,5-tri(lower alkoxy)tetrahydrofurans and their alcoholysates, beinghigh-boiling liquids, are useful as organic solvents for high temperature reactions, such as Grignard reactions, wherein usual solvents such as tetrahydrofuran are unavailable because of their lower boilingpoints. The 2,3,5-tri(lower alkoxy)tetrahydrofurans and their alcoholysates are also useful as intermediates in the preparation of the 6-lower alkoxy tropinones of this invention. Thus, 6-lower alkoxy 'tropin'es can be prepared by the hydrolysis of a mixture of tri(lower alkoxyfietrahydrofuran and (lower 'alkoxy)succinicdialdehyde tetra (lower alkyl) acetal, and reaction of the resulting solution of (lower alkoxy)suc,cinic dialdehyde with acetone dicarboXylic acid and methylamine to give a mixture of the cis and trans forms of racemic 6-lower alkoxy tropinones with different boiling points.

The following schemes of reaction will serve to illustrate this aspect of the invention:

CHZCOOH GHQ-CH0 C0 NHQGHB RO-OH-CHO 1 (nirvana-om NCH; 0

l I aoon-onom where R is a lower alkyl group including methyl, ethyl, propyl, etc. 7 The 6-lower alkoxy tropinones, thus formed, can then be cleaved to 6-hydroxytropinone by treating with aqueous hydrogen bromide in the known manner; or it can be converted to valeroidine by the lgnown reactions of reduction of the 3-keto group to hydroxy, esterification of the resultant 6-lower alkox'y-3-hydroxytropinone with valeryl chloride, and cleaving of the 6-lower alkoxy group to yield valeroidine.

The invention is illustrated by the following examples:

EXAMPLE 1 g. of 2,5-diethoxy2,S-dihydrofuran is dissolved in 560 cc. of anhydrous ethanol and 15 cc. of boron triuxed for 90 minutes at atmospheric pressure. A sodium ethoxide solution prepared from 7.5 g. of sodium and 60 cc. of ethanol is then added, and the reaction mixture is refluxed for a further 30 minutes. After cooling to room temperature the sodiiim borofiuoride is filtered off ,and washed with 40 cc. ofv ether, which is addedto the "filtrate. .The latter is then evaporated in vacuum from a not is divided into two fractions, one of which, amounting fluoride etherate is. added,..whereafter the mixture is reto 100 cc. boils at about l12113-C.;at21 mm. pressure of mercury and consists of amixtureof stereoisomeric 2,3,S-triethoxytetrahydrofurans, and the other witha boiling point-of about 146." C. at 21mm. pressure of mercury, amounting'to about 35 cc. consists of ethoxysuccinic dialdehydetetraethylacctal. H

EXAMPLE 2.

13 g. of 2,5-dimethoxy-2,5-dihydrofuran is' dissolved in 13 cc. of methanol. 0.2 cc. of acetyl chloride is added .of mercury.

and the mixture is refluxed for 10 minutes. of sodium methoxide, prepared from 0.065 g. of sodium and 5 cc. of methanol is added. The mixture is distilled in vacuum yielding about 14.2 g. of a mixture of acetals A solution boiling at approximately 74-108 C. at 13 mm. pressure EXAMPLE 3 '20 g. of 2,S-dimethoxy-2,5-dihydrofuran, 75 cc. of

methanol and 2 cc. of boron trifiuoride etherate are re- -fluxed for minutes, and the reaction mixture is worked of mercury.

up as described in Example 2. Yield about 25.9 g., boil-.

ing point approximately -112 C. at 14mm. pressure EXAMPLE 4 Synthesis of 6-ethoxytropinone 5.0 g. of a mixture of 2,3,S-triethoxytetrahydrofuran .and .ethoxysuccinic dialdehyde tetraethylacetal, B.P. "94-134 C. (13mm. Hg pressure) [prepared by the procedure of Example 1] are heated under reflux with 5 .z';

ml. of 0.1 normal hydrochloric acid and 25 ml. of water for about ten minutes andthe resulting solution brought cooling to room temperature. Then 13.0 g. of acetone to pH 5 with 1 normal sodium bicarbonate solution after dissolved in a small amount of water is added and the rei1 sultingmixture left standing at room temperature overnight. 250 g. of anhydrous potassium carbonate (or g. of anhydrous sodium carbonate) is then added in small portions with cooling and stirring and the mixture is continuously extracted with ether for 24 hours. The ethereal extract is dried with sodium sulfate, the ether evaporated 'and to the oily residue containing 6-ethoxytropinone is added a hot solution of 2.5 g. of picric acid in ml. of ethanol. After cooling, 4.86 g. of yellow prisms of picrate A, M.P. about 157-'l59 C., separates. After three crystallizations from ethanol the M.P. is about 160 161 C..and the yield approximately 3.75 g.

in a similar manner.

.After concentrationiof the mother liquor, 0.35 g. ofa

stereoisomer (picrate B) with a melting point of about -133 C. is obtained. After four crystallizations the M.P. is about 140-141 0.; mixed M.P. with pier-ate A is about 130 C.

Cleavage of picrate A."18 g. of picrate A is suspended in 80 ml. of water and 40 g. of potassium carbonate is added in portions with stirring and cooling. The free base is isolated in the usual way. The yield is 6.3 g., B.P. about 120-121 C. (9 mm. Hg pressure); r1 1.482.

Cleavage of picrate B.-This cleavage is carried out in the same way. as the cleavage of picrate A. The free base boils under 11 mm. pressure of mercury atabout -136 Cg-11 5 1.484.. I,

Resolution of base 41. 60 g, -of-;th e racemic base A as obtained above is resolved in the customary wayuwith the aid of d ta'rtaric acid. About 72 g. of the laevo base, B.P. about 129-130" C. ('14 mm.-Hg pressure), 21 1.482, [111 '19 (c.='1.01 in' 96% ethanol), and

In a like manner G-methoxytropin'one can be prepared as hereiubefore described by hydrolyzing 2,3,5-trimeth'- oxytetrahydrofuran and methoxysuccinic dialdehyde tetramethylacetal. The 6-propoxy derivative can be prepared The invention may be variously otherwise embodied within the scope of the appended claims.

I claim:

1. A method for the production of trialkoxytetrahy.- drofuraus and their alcoholysates comprising heating a 2,5-di(lower alkoxy)- 2,5-dihydrofuran with a loweral kanol in the presence of a strong acid, subsequently neutralizing the acid, and fractionally distilling the, reaction product.

2. The method of claim 1, in which the acid is boron trifiuoride. I

3. The method of claim 2, in which the alkauol is methanol.

4. The method of claim 2, in which the alcohol is ethanol.

5. The method of claim 1, in which the acid is hydro,-

' chloric acid.

6. A method for the production of trialkoxyletrahy- 'drofurans and their alcoholysates comprising heating a 2,5-di(lower alkoxy)-2,5-dihydrofuran with a lower alkanol in the presence of a strong acid, adding an alkali lower alkoxide to the reaction mixture and fractionally distilling the resulting mixture.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Beilstein, vol. 1, p. 896, second suppl. (1941).

Stoll et al.: Chem. Abs., vol. 48, pp. 12138-39 (1954).

Stoll et al.: Helv. Chim. Acta., 35, p. 1265 (published June 16, 1952-received April 19, 1952). 

1. A METHOD FOR THE PRODUCTION OF TRIALKOXYTETRAHYDROFURANS AND THEIR ALCOHOLYSATES COMPRISING HEATING A 2,5-DI(LOWER ALKOXY)-2,5DIHYDROFURAN WITH A LOWER ALKANOL IN THE PRESENCE OF A STRONG ACID, SUBSEQUENTLY NEUTRALIZING THE ACID, AND FRACTIONALLY DISTILLING THE REACTION PRODUCT.
 5. THE METHOD OF CLAIM 1, IN WHICH THE ACID IS HYDROCHLORIC ACID. 